The Philippine government fired off a protest to the Chinese embassy and sent a coast guard vessel to the area in the South China Sea after two Chinese vessels ordered the survey ship to leave on Wednesday, Aquino told reporters.

“The coast guard ship will ensure that our rights are protected by making sure that this survey ship, granted authority by our government, finish(es) its job,” he added.

Philippine foreign ministry spokesman Ed Malaya said the oil survey ship had since gone back to the area where it encountered the Chinese patrols.

The Philippines earlier said it also scrambled a military aircraft to the area during the incident, but no armed hostilities occurred as the patrol boats themselves moved off when the plane arrived.

China on Friday brushed aside Philippine complaints.

Sun Yi, spokesman for the Chinese embassy in Manila, did not comment directly on the incident when contacted by AFP, saying only that the mission was taking note of the reports.

But he insisted China had sovereignty over the disputed area, known as the Nansha islands by the Chinese and the Spratly islands elsewhere.

“I want to point out that since historical times China has had indisputable sovereignty over the Nansha islands and their adjacent waters,” Sun said.

The Spratly islands, a reputedly oil-rich chain of tiny islands and reefs in the South China Sea, are claimed in whole or in part by Brunei, China, Malaysia, the Philippines, Taiwan and Vietnam.

In a separate development, Vietnam on Friday said it had lodged a complaint against Chinese military exercises near the Spratlys, accusing its neighbor of violating its sovereignty after reports of Chinese naval activity.